SYDNEY • Australian military spy planes will start flying missions over the southern Philippines to help in the fight against Islamic militants terrorising the area, the government said yesterday.

Fighters linked to the Islamic State in Iraq and Syria (ISIS) group have been battling troops around Marawi city in Mindanao in a conflict that has killed hundreds.

Canberra, which has an extensive defence cooperation programme with Manila, said two high-tech AP-3C Orion aircraft will provide surveillance support to the Philippine military.

"The regional threat from terrorism, in particular from (ISIS) and foreign fighters, is a direct threat to Australia and our interests," said Defence Minister Marise Payne.

She recently spoke with her Philippine counterpart, Ms Delfin Lorenzana, about how Australia could help and "we agreed the best way to defeat terrorism in our region is for us to work together".

The versatile AP-3C Orions usually patrol maritime borders and played a prominent role in searching for the missing Malaysia Airlines plane MH370, which went down in the Indian Ocean off Australia in 2014.

Philippine President Rodrigo Duterte declared martial law across Mindanao, home to 20 million people, on May 23, immediately after fighters flying the ISIS flag rampaged through Marawi.

AGENCE FRANCE-PRESSE